Threaded tubular connection with progressive axial thread interference

ABSTRACT

A threaded connection includes at least one contact zone axially separated from threadings in which male and female elements are in sealed contact via bearing surfaces respectively constituted by a cambered surface and by a tapered surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a threaded tubular connection comprising a maletubular element comprising a male threading and a female tubular elementcomprising a female threading which cooperates by makeup with said malethreading, the axial width of the threads of said threadings and/or theintervals between said threads varying progressively along the axis ofthe connection over at least a portion of the axial length of thethreadings, such that the threads of each threading are housed with anaxial clearance in the intervals of the other threading at the start ofmakeup, said clearance progressively decreasing until it becomes zeroduring makeup.

2. Discussion of the Background

The term “sealed contact” as used here means contact between twosurfaces pressed hard against each other to produce a metal-to-metalseal, in particular a gas-tight seal.

Threaded connections of this type are well known, in particular for usein oil and gas wells. They generally have threads with a dovetailprofile as described, for example, in U.S. Re 30 647 and U.S. Re 34 467.They suffer from a number of drawbacks. Firstly, the geometricalcharacteristics of progressive interfering threads cannot ensure agas-tight seal. Such a seal is difficult to obtain with abutmentsurfaces separate from the threadings; sealing surfaces demand veryaccurate relative positioning of the two elements at the end of makeup.However, the final relative position of the elements is in this casestrongly influenced by the machining tolerances for the threads. The useof tapered sealing surfaces with a small taper and thus a small vertexangle, which are more tolerant as regards axial position, does notconstitute a satisfactory solution as such bearing surfaces areextremely sensitive to the phenomenon of galling, which result inspoiling after only a few makeup-breakout operations.

A further disadvantage of said known threaded connections is that thegeometric characteristics of the threadings do not encourage evacuationof the lubrication grease used for makeup. This grease can accumulatelocally, for example between the thread crests and roots, giving rise tovery high pressures which in their turn perturb proper positioning ofthe elements and contact of the sealing surfaces.

SUMMARY OF THE INVENTION

The invention aims to eliminate all of the drawbacks mentioned above andto maximize the axial effective contact length under load (internal orexternal pressure, axial tension or compression) of the sealingsurfaces.

The invention also aims to provide a threaded connection that resistscyclic mechanical loads (fatigue).

To this end, the invention provides a threaded connection of the typedefined in the introduction, comprising at least one contact zoneaxially separated from said threadings, in which the male and femaleelements are in sealed contact by means of bearing surfaces respectivelyconstituted by a cambered surface and by a tapered surface.

It has been shown that such a contact zone, which is known per se,allows a substantial variation in the axial position of the contact zoneand thus in the relative position of the elements without losing thegas-tight seal, the effective length of the contact zone or the integralof the contact pressure along the contact zone being high (contactstability).

Optional characteristics of the invention, which may be complementary orsubstitutional, are defined below:

-   -   The cambered surface has a generatrix with a radius of curvature        in the range 30 to 80 mm.    -   The tangent to the vertex half angle of the tapered surface is        in the range 0.025 to 0.075, corresponding to a taper in the        range 5% to 15%.    -   The contact zone is axially located between the threadings and        the free end of the male element.    -   The contact zone is axially located between the threadings and        the free end of the female element.    -   The contact zone is axially spaced from said free end by at        least 3 mm.    -   The cambered surface and the tapered surface are provided on the        element having said free end and on the other element        respectively.    -   The cambered surface extends in the direction of said free end        with a second tapered surface which is tangential to the        cambered surface.    -   The contact zone is axially located between two portions of each        of said threadings.    -   The cambered surface and the tapered surface are formed on the        male and female elements respectively.    -   The male and female elements are free of axial abutment        surfaces.    -   The axial width of the threads of said threadings and/or the        intervals between said threads varies progressively over the        whole of the axial length of said threadings.    -   The axial width of the threads of said threadings and/or the        intervals between said threads varies progressively over the        whole of the axial length of each of said threading portions.    -   Said threadings are tapered.    -   The tapered surfaces having lines joining homologous points on        the different turns as generatrices for the two portions of the        same threading respectively are substantially coincident.    -   The tapered surfaces having lines joining homologous points of        the different turns as generatrices respectively for the two        portions of the same threading are distinct.    -   Said tapered surfaces are radially distant by at least one        thread depth.    -   Said threads have a dovetail profile.    -   The crests and roots of said threads are parallel to the axis of        the threaded connection.    -   The male element is on a great length pipe and its minimum        radial thickness e between the portion of its threading that is        furthest from its free end and said contact zone is at least 60%        of the radial thickness E within the length of the pipe.    -   The connection comprises two contact zones situated respectively        in two of the axial positions as described above.    -   A groove formed at the crest of the male or the female threads        extends along the helical path thereof to allow evacuation of a        lubricant and terminates in an annular discharge space present        between the male and female elements at the end of the threading        or the threading portion concerned, to release the grease        pressure.    -   Said groove has a width of about 0.4 mm.    -   Said groove has a depth of about 0.4 mm.    -   For the male threading and/or the female threading, the loading        flank joins the crest and/or the root of the thread via a        rounded portion the profile of which is substantially formed by        two arcs of circles tangential to each other, the arc adjacent        to the loading flank having a smaller radius of curvature than        the other arc.    -   The radius of the arc adjacent to the loading flank is in the        range 0.1 to 0.2 mm.    -   The radius of said other arc is in the range 0.8 to 1.2 mm.    -   The male and female threadings are non interfering at the thread        roots and crests over all or a portion of the threadings.    -   The male and female threadings are interfering at the thread        roots and crests over all or a portion of threadings.    -   The male and female threadings are interfering at the thread        roots of a first threading and at the thread crests of a second        threading over all or a portion of the threading length whereas        there is a radial clearance between the thread roots of the        second threading and the thread crests of the first threading.    -   Said radial clearance is at least 0.05 mm

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the invention will now bedescribed in more detail in the description below, made with referenceto the accompanying drawings.

FIGS. 1 to 3 are half axial cross sectional views of three threadedtubular connections of the invention intended for oil or gas wells.

FIG. 4 is a partial view on a larger scale of a region of any one of theconnections of FIGS. 1 to 3 close to the free end of the male element.

FIGS. 5 and 6 are partial axial cross sectional views, on a still largerscale, each showing one thread of a connection of the invention.

FIG. 5A shows detail A of FIG. 5 on a larger scale.

FIGS. 7 and 8 show partial axial sectional views each showing a fewturns of the male and female threadings of a connection of the inventionin the made up position for non interfering and interfering threadingsrespectively.

FIG. 9 shows a partial sectional view showing a few turns of the malethreading of a connection of the invention, the axial width of thethreads and that of the intervals between the threads increasing anddecreasing respectively progressively from the free end of the maleelement.

FIG. 10 shows a variation of FIGS. 7 and 8.

FIG. 11 a is a partial axial cross section view of a first section of amale threading interfacing with a female crest and a female root at anearly stage of makeup.

FIG. 11 b is a partial axial cross section view of a second section ofthe male threading interfacing with the female crest and the female rootat an intermediate stage of makeup.

FIG. 11 c is a partial axial cross section view of a third section ofthe male threading interfacing with the female crest and the female rootat an end of makeup.

FIG. 12 is a partial view on a larger scale of contact zone 6 of FIG. 1that is formed by a cambered surface and a tapered surface on the femaleelement and the male element respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The threaded tubular connection shown in FIG. 1 comprises a male tubularelement 1 and a female tubular element 2 each on a great length pipe,not shown in its entirety, and provided with respective taperedthreadings 3, 4 which cooperate together for mutual assembly by makeupof the two elements. The threadings 3, 4 are of a known type with aprogressive variation in the axial thread width and/or the intervalsbetween threads so that a progressive axial interference occurs duringmakeup until a final blocked position.

In accordance with the invention, the fluid seal, both against theinterior of the tubular connection and against exterior media, isensured by two contact zones 5, 6 axially located either side of thethreadings 3, 4 respectively close to the free end 7 of the male elementand the free end 8 of the female element.

The contact zone 5 is shown on a larger scale in FIG. 4. To define saidcontact zone, male element 1 has a cambered surface 11 turned radiallyoutwardly, the diameter of which decreases towards the free end 7. Thesurface 11 has an arc of a circle as a generatrix, with a radius in therange 40 to 80 mm. Facing said cambered surface 11, the female element 2has a tapered surface 12 turned radially towards the interior and with adiameter that decreases in the direction of the free end 7 of the maleelement, i.e. opposite the free end 8 of the female element. The tangentto the vertex half angle of the tapered surface 12 is in the range 0.025to 0.075, i.e. a taper that is in the range 5% to 15%. For illustrativepurposes, the surfaces 11 and 12 are shown in FIG. 4 in their initialgeometric form before makeup but in a relative position corresponding tothe end of makeup of the threaded connection, so that their generatricesintersect one another. Clearly, in reality, progressive deformation ofsaid surfaces occurs during makeup, leading to a seal by radialinterference. The contact zone proper or effective contact zone betweensurfaces 11 and 12 has a certain length and terminates at a point Pwhich is spaced from the free end 7 by a distance d, advantageously atleast 3 mm.

The inventors have discovered that such a contact zone between a taperedsurface and a cambered surface produces a high effective axial contactwidth and a substantially parabolic distribution of contact pressuresalong the effective contact zone, in contrast to contact zones betweentwo tapered surfaces which have two narrow effective contact zones atthe ends of the contact zone.

A contact zone geometry of the invention preserves a good effectivecontact width despite axial positional variations of the assembledelements due to machining tolerances, the effective contact zonepivoting along the cambered section of the cambered surface 11,retaining a parabolic profile for the local contact pressure.

In this regard, it is an advantage that the axial length of the contactsurfaces 11, 12 be greater than the axial positioning variations of theeffective contact zone. Preferably the axial length of the contactsurfaces 11, 12 is greater or equal to 3.5 mm.

This is also the case under service conditions when the stresses towhich the threaded elements of the connection are subjected (inparticular internal or external pressure) induce pivoting of the contactsurfaces 11, 12.

The contact zone geometry of the invention appeared particularlyadvantageous for ensuring the seal when the connection is subjected to ahigh internal pressure after being subjected to a high externalpressure.

Too small a taper (<5%) for the surface 12 induces a risk of galling onmakeup and too high a taper (>15%) necessitates machining tolerancesthat are too narrow.

Too large a radius (>80 mm) for the cambered surface 11 inducesdisadvantages that are identical to those with a taper-to-taper contact.

Too low a radius (<30 mm) for said cambered surface 11 induces aninsufficient contact width.

A distance of at least 3 mm of point P from the free end 7 increases theradial stiffness of the male lip on which the cambered surface 11 isformed and can then increase the contact pressures for a given sectionof material at point P.

The distance d is preferably in the range 4 to 10 mm and in particular,varies with the pipe diameter.

In the example illustrated, the cambered surface includes a curvedcontact surface 44 which is curved along an axial direction as shown inFIG. 4. The cambered surface 11 of the male element extends beyond pointP and the curved contact surface 44 connects tangentially with a taperedsurface 13 with a vertex half angle of seven degrees which extends tothe free end 7 of said element, which is a flat surface perpendicular tothe axis of the threaded connection. The tapered surface 12 extendsbeyond point P and is followed by a backoff hollow 15 up to a shoulder14 of the female element facing end 7 and having a flat annular formperpendicular to the axis of the threaded connection.

The make up of the elements is not limited by any axial abutmentsurface. In particular surfaces 7 and 14 do not come into abutment anddo not play any role in the cooperation of elements 1 and 2. The backoffhollow between the tapered surface 12 and the shoulder 14 also plays norole in the cooperation of elements 1 and 2.

In contrast, the tapered surface between the cambered surface 11 and end7 can pre-centre the male element as it engages with the female elementprior to makeup without risking damage to the contact surfaces 11 and12.

Further, it can keep a sufficient thickness of material at the end 7 fora given distance between it and the point P with respect to a maleelement wherein the cambered surface 11 would extend to the free end.

At the other end of the cambered surface 11 is an annular groove 17which allows the male threading 3 to start.

Preferably, the thickness of the metal on the male element 1 at thebottom of said groove is at least 30% of the thickness of the pipe, toprevent radial deflection towards the axis of said zone.

The contact zone 6 is formed by a cambered surface 45 and a taperedsurface 46 with the same geometric characteristics as the surfaces 11and 12 of the zone 5, this time provided on the female element 2 and onthe male element 1 respectively. The cambered surface 45 includes acurved contact surface 47 which is curved along an axial direction. Anembodiment of the contact zone 6 is illustrated in FIG. 12 consistentwith FIG. 1. The effective contact zone is spaced from the free end 8 ofthe female element by a distance of at least 3 mm. The inventors haveestablished that such a distance can substantially increase the contactpressure in zones 5 and 6. The contact zone 5 provides the fluid-tightseal against the interior of the tubular connection and the contact zone6 provides the fluid-tight seal against external media.

In contrast to threadings 3 and 4 of FIG. 1, which are continuous, eachof the threadings of the tubular connection of FIG. 2 is separated intotwo portions separated from each other in the axial direction, namelyinto a male threading portion 3 a cooperating with a portion of thefemale threading 4 a, and a male threading portion 3 b cooperating witha portion of the female threading 4 b, portions 3 a and 4 a being closerto the free end 8 of the female element and portions 3 b and 4 b beingcloser to the free end 7 of the male element 1. The characteristicpoints of the thread profile, for example the roots of stabbing flanksof the threading portions 3 a and 3 b, are located on substantiallycoincident tapered surfaces and similarly for the threading portions 4 aand 4 b. The term “substantially coincident” means that said taperedsurfaces are separated by a radial distance that does not exceed a fewtenths of millimeters. The progressive variation in the axial width ofthe threads and/or the intervals between the threads occurs here foreach of the threading portions, advantageously over the entire length ofeach thereof.

The seal of the connection of FIG. 2 towards the interior is ensured bya contact zone 5 that is identical to that of FIG. 1. For the sealtowards the exterior, the contact zone 6 of FIG. 1 is replaced by anintermediate contact zone 16 located between the threading portions 3 aand 4 a and the threading portions 3 b and 4 b. The contact zone 16 isdefined by a cambered surface on the male element and a tapered surfaceon the female element with the geometrical characteristics as describedabove for the contact zone 5 in FIG. 1.

For dovetail threads (see below), the minimum radial thickness e of themale element 1 between its threading portion 3 a and the contact zone 16is at least 60% of the radial thickness E in the length of the greatlength pipe 10 of which it forms part. The inventors have establishedthat the geometry of dovetail threads increases the radial stiffness oftheir connection compared with threads that are commonly termed“trapezoidal”, in which the axial width reduces from the thread root tothe crest.

The tubular connection of FIG. 3 differs from that of FIG. 2 by a radialoffset between the threads of the threading portions 3 a and 4 a andthose of the threading portions 3 b and 4 b; the roots and crests of theloading flanks and the stabbing flanks of the threading threads 3 a and4 b are located on tapered surfaces with a larger diameter than those ofthreading portions 3 b and 4 b. Said radial offset is greater than theradial depth of the threads. The fluid-tight seal of said connection isprovided by an interior contact zone 5 similar to the contact zones 5 ofFIGS. 1 and 2 and by an intermediate contact zone 16 similar to that ofFIG. 2.

FIG. 5 is a partial sectional view through an axial plane of a maleelement of a threaded connection 1 of the invention, showing one thread18 of said element. Thread 18 has, in known manner, a dovetail profilewith thread crests and roots that are parallel to the axis of thethreaded connection and thus straight. Further, the loading flank 19 ofthe thread 18 joins the thread crest 20 and the adjacent thread root 21via respective rounded portions the first of which is shown on a largerscale in FIG. 5A. The profile of said rounded portion 22 is composed oftwo arcs of circles 23 and 24, arc 23 being tangential to the flank 19and having a radius R1 in the range 0.1 to 0.2 mm, and arc 24 beingtangential to arc 23 and to the thread crest 20 and having a radius R2in the range 0.8 to 1.2 mm. Rounded portion 25 connecting the loadingflank 19 to the thread root 21 is similar to rounded portion 22, thecircular arc with the smaller radius also being adjacent to the flank19. These rounded portions reduce the load concentration factor at thebase of the loading flanks and thus improve the fatigue behaviour ofsaid connection.

FIG. 6 is a view analogous to FIG. 5, showing a groove 28 provided inthe thread crest 20. Said groove has a width l and a depth h, andextends over the whole of the helical path of the male threading to anannular discharge groove 17 (FIGS. 1, 2 and 4) at the end of thethreading or the threading portion to encourage evacuation of the greaseused for lubrication during makeup and as a result to release thepressure developed by said grease. Groove 28 also slightly increases theflexibility of the threads, rendering the relative axial position of themale and female elements less dependent on machining tolerances. In theexample shown, groove 28 is connected to the thread crest via roundedportions. These can be replaced by chamfers.

Rounded portions similar to rounded portions 22 and 25 and/or a groovesimilar to groove 28 can be provided on the female element in additionto or to replace those of the male element. Further, while the roundedportions and the groove are shown separately in FIGS. 5 and 6, they canadvantageously be used together, as shown in FIG. 9. It is also possibleto connect the loading flank of the threads of the male element and/orthe female element to only the thread crest or the root. A furtherpossible variation consists of providing a single contact zone ensuringa seal to both interior and exterior fluids.

The threadings employed in the embodiments can be of any non interferingtype between thread crests and roots, or of the interfering type betweenthread crests and roots.

FIG. 7 shows a male threading 3 and a female threading 4 in the made upposition in the case of non interfering threadings.

The male loading flanks 19 and female loading flanks 30 are in contact,as are the male stabbing flanks 31 and female stabbing flanks 32.

In contrast, there is a clearance 35 between the male and thread crest20 and the female thread root 33 as well as between the female threadcrest 34 and the male thread root 21.

Said function is obtained by causing the loading flanks and stabbingflanks to come into contact before any contact between the thread rootsand crests.

It can be seen that by dint of said clearances, a substantial helicalleakage channel 35 exists for fluids, even in the absence of a groove28, the seal being formed by contact surfaces 5, 6, 16.

FIG. 8 shows a male threading 3 and a female threading 4 in the made upposition in the case of interfering threadings; the reference numbersused in FIG. 7 are used to designate similar elements.

The threadings are designed so that the female thread crests come intocontact with the male thread roots and/or the male crests with thefemale thread roots during makeup before contact of the loading flanksand the stabbing flanks.

FIGS. 11 a, 11 b, and 11 c illustrate a female thread crest 34 and afemale thread root 33 as they interface with a male tubular element 1through different stages of makeup for one embodiment of the instantinvention. FIG. 11 a shows the female element 2 early in the makeupprocess where there is a radial clearance 35 between the female threadroot 33 and the male thread crest 20, as well as a radial clearance 35between the female thread crest 34 and the male thread root 21. The malethread crest 20 and male thread root 21 are represented in FIG. 11 a asbeing part of a first section 41 of the male threading 3 as found onmale tubular element 1. The axial clearances 37 are a first axialclearance distance between the female stabbing flank 32 and the malestabbing flank 31 as well as a second axial clearance distance betweenthe female loading flank 30 and the male loading flank 19.

FIG. 11 b shows the same female thread root 33 and female thread crest34 as in FIG. 11 a, but the male tubular element 1 has rotated relativeto female element 2 and the female thread root 33 and crest 34 areexposed to a second section 42 of the male threading 3 and are nearer tothe achieving end of makeup as compared to FIG. 11 a. In the moreadvanced stage of makeup in FIG. 11 b, the axial clearances 37 stillhave not been decreased to zero, but the radial clearances 35 havedecreased to zero. At the end of makeup represented in FIG. 11 c theaxial clearances have decreased to zero where the female thread root 33and crest 34 are exposed to a third section 43 of the male threading 3.

FIGS. 11 a, 11 b, and 11 c also illustrate an axial width of the malethread 40 and the interval between the male thread 39 varyingprogressively along an axis of connection over at least a portion of anaxial length of the threadings. In FIG. 11 a, the axial width of a malethread 40 increases successively from FIG. 11 a to FIG. 11 b to when theaxial width 40 fills up the corresponding female crest 33 in FIG. 11 cresulting in zero axial clearances 37. An interval 39 between malethreads decreases a corresponding amount with every increase in theaxial width 40 of a male thread 38 as shown in FIGS. 11 a, 11 b, and 11c.

After said contact between the thread crests and roots, makeup can becontinued until the loading and stabbing flanks come into contact; thethread crests will interfere with the corresponding thread roots.

However, calculations carried out by the inventors show that asufficient seal cannot be guaranteed (gas-tight seal) by threads of thattype of threading because of deformations in the thread faces and theangles between the faces at the end of makeup.

The presence of a groove will also increase the cross section of theleakage channels resulting from said deformations. As was the case withnon interfering threadings, the seal with interfering threadings is madeby the contact surfaces 5, 6, 16.

One advantage of interfering threadings is to use, for a constant pipethickness, higher critical cross sections and as a result, to entrainhigher efficiency of the threaded connection under tension.

FIG. 10 is similar to FIGS. 7 and 8 and again bears the same referencesin the case of interfering threadings at the male thread roots 21 and atthe female thread crests 34, a radial clearance 35 existing between thefemale thread roots 33 and the male thread crests 20. Of course one canprovide for the reverse disposition, i.e. a clearance between the malethread roots 21 and the female thread crests 34 and an interferencebetween the female thread roots 33 and the male thread crests 20.

It is also possible to have 2 or more of the dispositions of FIGS. 7, 8and 10 and of reversed FIG. 10 on the various portions of the threadinglength for example as in the embodiments of FIGS. 2 and 3 where thethreadings are in two portions.

This explains why in FIG. 2 the tapered surfaces of the two threadingportions only need to be substantially coincident, the interferencedifference between the portions inducing a slight radial distancebetween these surfaces.

By way of example, the dispositions of FIGS. 7 and 8 can be producedwith male threads and female threads of a uniform height to 1.16±0.025mm, and the disposition of FIG. 10 by increasing the female threadheight of 1.285±0.025 mm, the male thread height remaining unchanged,which leads to a radial clearance ≧0.075 mm between male crests andfemale roots.

FIG. 9 shows a few turns of the thread 18 of the male threading of aconnection of the invention, separated from each other by a helicalinterval 36. It illustrates the progressive variation, known per se, ofthe axial width of the thread 18 and that of the interval 36,respectively increasing and reducing from the free end of the maleelement, which causes progressive axial interference of the male andfemale threads during makeup.

The embodiments of FIGS. 1 to 3 are relative to threaded assembliesbetween two great length pipes constituted by only one threadedconnection the male and female tubular elements of which are located atthe end of the great length pipes.

Such threaded assemblies can be of the “flush” type (the externaldiameter of both elements of the threaded connection is that of thepipe) or of the “semi-flush” type also known as “slim-line” (theexternal diameter of the female element is greater by a few percent thanthe diameter of the male element).

The invention can also apply to threaded and coupled assemblies betweentwo great length pipes, those coupled assemblies being constituted bytwo tubular threaded connections, the female elements being positionedopposite on a coupling whereas the male elements are produced on greatlength pipes.

1. A threaded tubular connection, comprising: a male tubular elementhaving a male threading, the male threading including a male helicalscrew thread including a male crest, a male root, a male free end thatis a flat surface perpendicular to an axis of the threaded connection, amale stabbing flank, and a male loading flank; a female tubular elementcomprising a female threading that cooperates by makeup with the malethreading, an axial width of the threads of the male threading and thethreads of the female threading and intervals between the threadsvarying progressively along an axis of connection over at least aportion of an axial length of the male threading and the femalethreading, the male threading and the female threading being configuredsuch that the threads of each of the male threading and the femalethreading are housed with an axial clearance in the intervals of theother threading at a staff of makeup, the axial clearance progressivelydecreasing until the axial clearance becomes zero at an end of makeup,the female threading being a female helical screw thread including afemale crest, a female root, a female free end that is a flat surfaceperpendicular to the axis of the threaded connection, a female stabbingflank, and a female loading flank; and at least one contact zone axiallyseparated from the male threading and the female threading wherein themale and female elements are in sealed contact by bearing surfacesconstituted by a cambered surface and by a tapered surface, the at leastone contact zone including a first contact zone, the first contact zoneincluding the cambered surface having a curved contact surface incontact with the tapered surface, the curved contact surface beingcurved along an axial direction, wherein the male free end does not abutthe female tubular element and the female free end does not abut themale tubular element.
 2. The threaded tubular connection according toclaim 1, wherein the curved contact surface has a generatrix with aradius of curvature in a range of 30 to 80 millimeters.
 3. The threadedtubular connection according to claim 2, wherein a trigonometric tangentto a vertex half angle of the tapered surface is in a range of 0.025 to0.075.
 4. The threaded tubular connection according to claim 1, whereinthe first contact zone is axially disposed between the male threadingand the female threading and the free end of the male element.
 5. Thethreaded tubular connection according to claim 4, wherein the firstcontact zone is axially spaced from the free end by at least threemillimeters.
 6. The threaded tubular connection according to claim 4,wherein the cambered surface and the tapered surface are provided on themale tubular element having the male free end and on the female tubularelement respectively.
 7. The threaded tubular connection according toclaim 6, wherein the cambered surface extends in a direction of the malefree end with a second tapered surface that is tangential to thecambered surface.
 8. The threaded tubular connection according to claim1, wherein the first contact zone is axially disposed between the malethreading and the female threading and the free end of the femaleelement.
 9. The threaded tubular connection according to claim 1,wherein the male helical screw thread includes a first portion and asecond portion and the female helical screw thread includes a firstportion and a second portion respectively configured to interface withthe first portion and the second portion of the male helical screwthread, and wherein the first contact zone is axially located betweenthe first portion and the second portion of the male helical screwthread.
 10. The threaded tubular connection according to claim 9,wherein the cambered surface and the tapered surface belong to the firstportion and the second portion of the male helical screw thread and thefirst portion and second portion of the female helical screw threadelement respectively.
 11. The threaded tubular connection according toclaim 9, wherein the axial width of the threads of the male threadingand the threads of the female threading and the intervals between thethreads of the male threading and the threads of the female threadingvary progressively over the whole of the axial length of each of thefirst portion and the second portion of the male helical screw thread.12. The threaded tubular connection according to claim 9, wherein thefirst portion and the second portion of the male helical screw threadare tapered.
 13. The threaded tubular connection according to claim 12,wherein the tapered surfaces having lines joining homologous points ondifferent turns as generatrices for the first portion and the secondportion of the male helical screw thread are substantially coincident.14. The threaded tubular connection according to claim 12, wherein thetapered surfaces having lines joining homologous points on differentturns as generatrices for the first portion and the second portion ofthe male helical screw thread respectively are distinct.
 15. Thethreaded tubular connection according to claim 14, wherein the firstportion and the second portion of the male helical screw thread areradially distant by at least one thread depth.
 16. The threaded tubularconnection according to claim 1, wherein the axial width of the threadsof the male threading and the threads of the female threading and theintervals between the threads of the male threading and the threads ofthe female threading vary progressively over a whole of the axial lengthof the male threading and the female threading.
 17. The threaded tubularconnection according to claim 1, wherein the male threading and thefemale threading have a dove-tail profile.
 18. The threaded tubularconnection according to claim 17, wherein the male crest, the male root,the female crest, and the female root are parallel to the axis of thethreaded connection.
 19. The threaded tubular connection according toclaim 18, wherein the male element is on a length pipe having a minimumradial thickness between a portion of the threading of the male elementfurthest from the free end of the male element and the first contactzone is at least 60% of a radial thickness within the length of thepipe.
 20. The threaded tubular connection according to claim 18, whereinfor the male threading and the female threading, a loading flank joinsthe thread crest at a rounded portion at an intersection of the threadcrest and loading flank, the rounded portion being substantially formedby a first arc of a circle and a second arc of a circle tangent to eachother, the first arc being also tangent to the loading flank, and thesecond arc being tangent to the thread crest, the first arc having asmaller radius of curvature than the second arc.
 21. The threadedtubular connection according to claim 20, wherein the radius of the arcadjacent to the loading flank is in a range of 0.1 to 0.2 millimeters.22. The threaded tubular connection according to claim 21, wherein theradius of the other arc is in a range of 0.8 to 1.2 millimeters.
 23. Thethreaded tubular connection according to claim 18, wherein the malethreading and the female threading are non interfering at the threadroots and crests over all or a portion of the male threading and thefemale threading.
 24. The threaded tubular connection according to claim18, wherein the male threading and the female threading interfere at thethread roots and crests over all or a portion of the male threading andthe female threading.
 25. The threaded tubular connection according toclaim 18, wherein the male threading and the female threading interfereat the thread roots of a first threading and at the thread crests of asecond threading over all or a portion of the threading length, whereasthere is a radial clearance between the thread roots of the secondthreading and the thread crests of the first threading.
 26. The threadedtubular connection according to claim 25, wherein said radial clearanceis at least 0.05 millimeters.
 27. The threaded tubular connectionaccording to claim 1, wherein the threaded connection also comprises asecond contact zone including a second cambered surface in sealedcontact with a second tapered surface, the second cambered surface atthe second contact zone having a second curved contact surface incontact with the second tapered surface, the second cambered surfaceattached to the female element, the second tapered surface attached tothe male element, and the second curved contact surface being curvedalong an axial direction.
 28. The threaded tubular connection accordingto claim 27, wherein the second cambered surface and the second taperedsurface have a substantially parabolic distribution of contact pressuresalong said second contact zone.
 29. The threaded tubular connectionaccording to claim 1, wherein a groove formed at the crest of the malethreads or the female threads extends along a helical path thereof toallow evacuation of a lubricant and terminates in an annular dischargespace present between the male element and the female element at the endof the threading or the threading portion concerned.
 30. The threadedtubular connection according to claim 29, wherein the groove has a widthof about 0.4 millimeters.
 31. The threaded tubular connection accordingto claim 30, wherein the groove has a depth of about 0.4 millimeters.32. The threaded tubular connection according to claim 1, wherein thecambered surface and the tapered surface have a substantially parabolicdistribution of contact pressures along said first contact zone.
 33. Thethreaded tubular connection according to claim 1, wherein said camberedsurface is separated from the male threading and the female threading byan annular groove.
 34. A threaded tubular connection, comprising: a maletubular element comprising a male free end that is a flat surfaceperpendicular to an axis of the threaded connection and a male threadingand a female tubular element comprising a female free end that is a flatsurface perpendicular to the axis of the threaded connection and afemale threading that cooperates by makeup with the male threading, anaxial width of threads of the male threading and the female threadingand intervals between the male thread and the female thread varyingprogressively along an axis of connection over at least a portion of anaxial length of the male threading and the female threading, such thatthe threads of each of the male threading and the female threading arehoused with an axial clearance in the intervals of the other threadingat a start of makeup, the clearance progressively decreasing until itbecomes zero at an end of makeup; and at least one contact zone axiallyseparated from the male threading and the female threading in which themale element and the female element are in sealed contact by bearingsurfaces respectively constituted by a cambered surface and by a taperedsurface, the at least one contact zone including a first contact zone,the first contact zone including the cambered surface having a curvedcontact surface in contact with the tapered surface, the curved contactsurface being curved along an axial direction, wherein the male free enddoes not abut the female tubular element and the female free end doesnot abut the male tubular element and said contact zone is pivotablealong said curved contact surface in response to axial positionalvariations of said male tubular element and said female tubular element.35. A threaded tubular connection, comprising: a male tubular elementhaving a male threading, the male threading including a male crest, amale root, a male loading flank, and a male stabbing flank; a femaletubular element having a female threading which cooperates by makeupwith said male threading, an axial width of the threads of said malethreading and said female threading and the intervals between saidthreads of said male threading and said female threading varyingprogressively along the axis of the connection over at least a portionof the axial length of the male threading and the female threading, suchthat the threads of each of the male threading and the female threadingare housed with an axial clearance in the intervals of the otherthreading at a start of makeup, said clearance progressively decreasinguntil it becomes zero at an end of makeup in a final position of themale and the female threading, the female threading including a femalecrest, a female root, a female loading flank, and a female stabbingflank; and at least one contact zone axially separated from saidthreadings in which the male element and the female element are insealed contact by means of bearing surfaces respectively constituted bya cambered surface and by a tapered surface, the at least one contactzone including a first contact zone, the first contact zone includingthe cambered surface having a curved contact surface in contact with thetapered surface, the curved contact surface of being curved along anaxial direction, wherein a trigonometric tangent to a vertex half angleof the tapered surface is in the range of 0.025 to 0.075, and thecontact is a sealed metal-to-metal contact being effective in said finalposition of the male and the female threading.